1 2 /* @(#)e_fmod.c 1.3 95/01/18 */ 3 /* 4 * ==================================================== 5 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 6 * 7 * Developed at SunSoft, a Sun Microsystems, Inc. business. 8 * Permission to use, copy, modify, and distribute this 9 * software is freely granted, provided that this notice 10 * is preserved. 11 * ==================================================== 12 */ 13 14 #include <sys/cdefs.h> 15 __FBSDID("$FreeBSD$"); 16 17 /* 18 * fmod(x,y) 19 * Return x mod y in exact arithmetic 20 * Method: shift and subtract 21 */ 22 23 #include <float.h> 24 25 #include "math.h" 26 #include "math_private.h" 27 28 static const double one = 1.0, Zero[] = {0.0, -0.0,}; 29 30 double 31 fmod(double x, double y) 32 { 33 int32_t n,hx,hy,hz,ix,iy,sx,i; 34 u_int32_t lx,ly,lz; 35 36 EXTRACT_WORDS(hx,lx,x); 37 EXTRACT_WORDS(hy,ly,y); 38 sx = hx&0x80000000; /* sign of x */ 39 hx ^=sx; /* |x| */ 40 hy &= 0x7fffffff; /* |y| */ 41 42 /* purge off exception values */ 43 if((hy|ly)==0||(hx>=0x7ff00000)|| /* y=0,or x not finite */ 44 ((hy|((ly|-ly)>>31))>0x7ff00000)) /* or y is NaN */ 45 return nan_mix_op(x, y, *)/nan_mix_op(x, y, *); 46 if(hx<=hy) { 47 if((hx<hy)||(lx<ly)) return x; /* |x|<|y| return x */ 48 if(lx==ly) 49 return Zero[(u_int32_t)sx>>31]; /* |x|=|y| return x*0*/ 50 } 51 52 /* determine ix = ilogb(x) */ 53 if(hx<0x00100000) { /* subnormal x */ 54 if(hx==0) { 55 for (ix = -1043, i=lx; i>0; i<<=1) ix -=1; 56 } else { 57 for (ix = -1022,i=(hx<<11); i>0; i<<=1) ix -=1; 58 } 59 } else ix = (hx>>20)-1023; 60 61 /* determine iy = ilogb(y) */ 62 if(hy<0x00100000) { /* subnormal y */ 63 if(hy==0) { 64 for (iy = -1043, i=ly; i>0; i<<=1) iy -=1; 65 } else { 66 for (iy = -1022,i=(hy<<11); i>0; i<<=1) iy -=1; 67 } 68 } else iy = (hy>>20)-1023; 69 70 /* set up {hx,lx}, {hy,ly} and align y to x */ 71 if(ix >= -1022) 72 hx = 0x00100000|(0x000fffff&hx); 73 else { /* subnormal x, shift x to normal */ 74 n = -1022-ix; 75 if(n<=31) { 76 hx = (hx<<n)|(lx>>(32-n)); 77 lx <<= n; 78 } else { 79 hx = lx<<(n-32); 80 lx = 0; 81 } 82 } 83 if(iy >= -1022) 84 hy = 0x00100000|(0x000fffff&hy); 85 else { /* subnormal y, shift y to normal */ 86 n = -1022-iy; 87 if(n<=31) { 88 hy = (hy<<n)|(ly>>(32-n)); 89 ly <<= n; 90 } else { 91 hy = ly<<(n-32); 92 ly = 0; 93 } 94 } 95 96 /* fix point fmod */ 97 n = ix - iy; 98 while(n--) { 99 hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1; 100 if(hz<0){hx = hx+hx+(lx>>31); lx = lx+lx;} 101 else { 102 if((hz|lz)==0) /* return sign(x)*0 */ 103 return Zero[(u_int32_t)sx>>31]; 104 hx = hz+hz+(lz>>31); lx = lz+lz; 105 } 106 } 107 hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1; 108 if(hz>=0) {hx=hz;lx=lz;} 109 110 /* convert back to floating value and restore the sign */ 111 if((hx|lx)==0) /* return sign(x)*0 */ 112 return Zero[(u_int32_t)sx>>31]; 113 while(hx<0x00100000) { /* normalize x */ 114 hx = hx+hx+(lx>>31); lx = lx+lx; 115 iy -= 1; 116 } 117 if(iy>= -1022) { /* normalize output */ 118 hx = ((hx-0x00100000)|((iy+1023)<<20)); 119 INSERT_WORDS(x,hx|sx,lx); 120 } else { /* subnormal output */ 121 n = -1022 - iy; 122 if(n<=20) { 123 lx = (lx>>n)|((u_int32_t)hx<<(32-n)); 124 hx >>= n; 125 } else if (n<=31) { 126 lx = (hx<<(32-n))|(lx>>n); hx = sx; 127 } else { 128 lx = hx>>(n-32); hx = sx; 129 } 130 INSERT_WORDS(x,hx|sx,lx); 131 x *= one; /* create necessary signal */ 132 } 133 return x; /* exact output */ 134 } 135 136 #if (LDBL_MANT_DIG == 53) 137 __weak_reference(fmod, fmodl); 138 #endif 139